There's still something which could be improved (for instance, the minimap is a bit overdithered) and probably I'll be adding some extra stuff later (the glove cursors look pretty bad, but I've not managed to make a good looking one...).

Besides that, the pieces themselves should be pretty self explanatory.

I used Dawnbringer's 32 color palette, except for the orange and yellow colours which come from the 16 color palette (it was not feeling right with the ones from the 32 palette...), so the total colour count is 34.

No, the source code is not directly effected. But if you for example make a video of the game where this GUI is shown, the video as a whole would have to be CC-by-SA.

That said, in general if someone puts his artwork under this license, it is implied that the use in closed source projects is not really favoured, or are you just concerned about copyleft incompatibility with the GPL for example? For the latter it is no problem, you can have GPL code and CC-by-SA graphics (but IANAL).